Method of improving steam-assisted oil recovery

ABSTRACT

A method of improving hydrocarbon recovery from a hydrocarbonbearing formation in a steam injection operation by uniformly heating the perforated well liner adjacent a producing formation into which steam is to be injected prior to injecting steam through the liner into the formation.

United States Patent [72] Inventor Stanley 0.1-lutchison Bakersfield, Calif.

[21] App]. No. 824,577

[22] Filed May 14, 1969 [45] Patented June 8, 1971 [73] Assignee Chevron Research Company San Francisco, Calif.

[54] METHOD OF IMPROVING STEAM-ASSISTED OIL RECOVERY Y 2 Claims, 1 Drawing Fig.

[52] US. Cl 166/303 [51] Int. Cl E2lb43/24 [50] Field of Search 166/302,

[5 6] References Cited UNITED STATES PATENTS 3,352,359 11/1967 Sutliffet al. 166/53 3,392,783 7/1968 Reed 166/303 3,420,298 l/l 969 Cornelius 166/303X Primary Examiner-Ian A. Calvert Attorneys-A. L. Snow, F. E. Johnston, R. L. Freeland, Jr. and

E. J. Keeling ABSTRACT: A method of improving hydrocarbon recovery from a hydrocarbon-bearing formation in a steam injection operation by uniformly heating the perforated well liner adjacent a producing formation into which steam is to be injected prior to injecting steam through the liner into the formation.

STEAM SOURCE PATENTEU JUN 8 1971 STEAM SOURCE IN V ENTOR STANLEY 0. HUTCHISON METHOD OF IMPROVING STEAM-ASSISTED OIL RECOVERY This invention relates to improving the recovery of hydrocarbons from a hydrocarbon-bearing formation utilizing steam injection into such formation to promote oil recovery therefrom and, more particularly, this invention relates to an improved mode of promoting relatively uniform steam injection into a hydrocarbon-bearing formation penetrated by a well having a well liner placed therein by means of uniformly elevating the temperature of the liner to approximately steam injection temperature prior to injecting substantial amounts of steam through the liner into the formation.

Many methods utilizing steam have heretofore been advanced to assist the recovery of oil from oil-bearing formations. The use of steam, while known in the art for some time, has only recently become a generally used technique for assisting oil recovery. Steam has heretofore been suggested as a heating medium for use in a single well stimulation operation. This type of operation is known in the art as huff and puff. in the huff and puff operation steam is injected for a time through a well into an oil-bearing formation and then injection is halted and a period of time is allowed for soaking or heating the formation some distance beyond the well. After the soak period the injection well is converted to a production well and oil is produced through the heated zone and up the well. Steam has also been heretofore utilized in a steam flood or steam drive operation. in this type of operation, steam is injected into a formation through one or more injection wells and driven through a formation to improve oil recovery at one or more remote production wells. in both of the abovedescribed operations, i.e., a single well huff and puff operation and a multiple well steam drive operation, it has been found that a serious problem arises because of the tendency of the injected steam to preferentially flow into only a portion of the hydrocarbon-bearing formation which, for one reason or another, has a higher permeability than the rest of the producing formation. Most steam promoted secondary recovery operations occur in producing intervals which may be as thick as 50 to 100 feet and often 200 to 400 feet or more. Thus a serious problem occurs when 70 to 80 percent or more of the steam enters only feet or so of the formation. When such an undesirable injection profile occurs the efficiency of the steam project is lost. It is thus a serious and still unsolved problem to promote entry of injected steam in substantially uniform amounts over the entire interval of the formation where stimulation is desired.

The present invention provides a method for promoting more uniform entry of steam through a well liner into a hydrocarbon-producing formation adjacent such liner by initially increasing the temperature of the well liner adjacent the producing formation to a temperature approaching the injection temperature of the steam which is to be injected into such formation prior to injecting substantial amounts of steam through such liner into the formation and, after such well liner reaches the elevated temperature, then injecting steam through the liner into the formation to promote the recovery of hydrocarbons from the formation. The steam injection profile when steam is injected through such a uniformly heated liner is usually greatly improved over injection profiles when prior methods of steam injection are used.

Thus in accordance with the invention it is important that the liner be heated uniformly to temperature before a substantial amount of steam is injected through the liner. The uniform heating of the liner before steam is injected into the formation removes viscous deposits or the like from substantially all the perforations of the liner and permits later-injected steam to enter all these perforations initially at substantially the same time. The viscous oil in the entire vertical extent of the producing formation adjacent the liner is thus contacted uniformly by the steam and the viscosity of such oil is uniformly reduced to promote steam to more uniformly enter the entire vertical extent of the formation to thus produce a more uniform steam injection profile. Once such an initial profile has been established there is high likelihood of a successful steam operation. This is contrasted by the methods used heretofore in which steam was injected into a formation through a cold liner and in which the steam very often initially entered a limited high permeability portion of the formation. Once the steam did enter such a portion it reduced the viscosity of the oil therein further reducing the resistance to steam flow in such portion, thus permitting more steam to enter. Once this viscous cycle has started the chances of obtaining relatively uniform steam injection are remote.

In a particular aspect, the present invention provides for uniformly heating a well liner located in a well adjacent a producing formation prior to injecting steam into such formation. The well liner is uniformly heated over its entire length by injecting steam into the well adjacent the lower portion of the well liner and circulating such steam up the well in contact with the liner to uniformly increase the temperature of the liner. After the liner has been uniformly heated by the circulation of steam such circulation is terminated and steam is injected through the perforations of the liner and out into the formation to promote the recovery of oil from the formation.

In the preferred form of the invention in which it is desired to promote relatively uniform injection of steam through a perforated well liner located in a well adjacent a producing formation, a well tube is inserted into the well and is lowered to a position adjacent the lower portion of the well liner. The tube provides a flow path for steam from the surface to a position adjacent the lower portion of the well liner. A second flow path in the well to the surface is provided by the annulus between such well tube and the well liner and the well casing located above the liner. After the flow tube is positioned so that the lower end thereof is adjacent the lower portion of the well liner, steam is injected from the surface down the flow tube into the well adjacent the lower portion of the well liner. The liner (casing)-tube annulus at this time is open to atmosphere at the surface thus causing the injected steam to circulate up such annulus adjacent the well liner to uniformly heat the liner. Injection in this manner is continued until the temperature of the well liner adjacent the producing formation is elevated to approximately the temperature of the steam which is to be injected into the formation. After the well liner has been so heated, the tubing-liner (casing) annulus is closed by appropriate means and steam is injected down the well through the perforations in the liner and out into the formation to promote the recovery of hydrocarbons from such formation.

It is an object of the present invention to provide a method of promoting relatively uniform injection of steam into a hydrocarbon formation penetrated by a well having a perforated liner located adjacent such formation.

Additional objects and advantages of the present invention will become apparent from the following detailed description read in light of the accompanying drawing which is made a part of this specification and which illustrates the preferred embodiment of apparatus assembled in accordance with the present invention.

The drawing shows an elevation view, partially in section, of a well penetrating an oil-producing formation 10. A portion of the well adjacent producing formation 10 contains a perforated or otherwise suitably slotted well liner 12. The well liner 12 is connected by suitable means to a string of casing 14 which extends from the upper portion of producing formation 10 through the earth to the surface. A tubing string 24 is located in the well and terminates adjacent the lower portion of the perforated well liner 12. The tubing string 24 thus provides a flow path from the surface to a position in the well adjacent the lower end of the producing formation 10 which is lined by perforated well liner 12. A second flow path from the lower part of the producing formation 10 is provided by the liner (casing)-tubing annulus 23. This flow path may be opened to atmosphere through blooie line 41. Flow through blooie line 4] is controlled by means of valve 43.

The tubing string 24 enters the well through a suitable wellhead 28. A baseplate 30 is connected to the top of the wellhead 28 and a set of slips 3] are used to hold the tubing string 28 during makeup of the string as is known in the art. Stripper rubber 35 is used in the wellhead to prevent leakage of fluid past the tubing string 24 where it enters the wellhead. A source of steam 32 is connected to the tubing string 24 by suitable means such as steam hose 34 and pipe 36. Appropriate valves 33 and 38 and connections 40 and 42 are provided on the steam line. The connections 40 and 42 are preferably hammer-type joints to facilitate makeup and breakup of the steam connection even while the pipes are hot. The steam line 36 is connected to the tubing string 24 by a suitable right angle connector 46. A lifting means for lowering or raising the tubing string in the well is provided by a hoist means which includes a traveling block 58 which is moved by suitable cables 60. A conventional hoist means or derrick not shown is used to move the traveling block 58 up or down. The angle connection 46 and the upper end of the tubing string 24 is held in an elevator 62 which is connected by suitable links 64 to the traveling block 58. Thus when the traveling block 58 moves up or down, the tubing string and the apparatus connected thereto are also raised or lowered.

In accordance with the preferred form of the invention, it is necessary prior to the injection of steam into formation to uniformly elevate the temperature of the liner 12 to approximately the temperature of the liner 12 to approximately the temperature desired for steam injection into formation 10. In order to accomplish this in an efficient manner, the tubing string is positioned in the well so that the lower end of the tubing string is located adjacent the lower end of the producing formation 10 into which it is desired to inject steam. The linercasing (tubing) annulus is opened to atmosphere by opening valve 43 on blooie line 41. Steam is injected down the well through tubing string 24 from steam source 32. The steam enters the well adjacent the lower portion of the producing formation 10. Because the tubing-liner (casing) annulus is opened to atmosphere, the steam is caused to flow up the annulus adjacent well liner 12 to provide for uniform heating of the liner [2. This insures that the liner 12 is uniformly heated over its entire length.

Steam circulation up the annulus in the above-described manner is continued for a time sufficient to heat the entire portion of the liner through which steam is to be injected into the producing formation 10. The amount of steam required to elevate the temperature of the liner to approximately the temperature of the steam is dependent upon a number of factors including the temperature of the formation adjacent the liner, the amount of fluid in the well, the liner length and the depth of the well. Generally steam is circulated for between I and 4 hours to satisfactorily elevate the temperature of most conventional liners. Steam is preferably injected at a rate between 1,000 and 1,400 equivalent barrels of water per day. Typical steam injection pressures are preferably in the range of about 400 p.s.i. Steam temperatures at the wellhead are usually in the 300500 F. range. However, steam at a temperature as low as 212 F. could be used in certain conditions. An indication that the perforated liner 12 is uniformly heated to steam temperature is given when steam is vented from the blooie line. This indicates that not much condensation is occurring downhole and that, therefore, the downhole environment including the well liner has been brought up to steam temperature. It is also possible, of course, to locate temperature measuring means such as one or more thermocouples adjacent the liner to accurately detect the temperature increase in the liner. However, the method of monitoring steam returns at the blooie line has been found satisfactory for most applications of the invention.

After the well liner has been brought up to temperature as indicated above, steam is injected through the perforations of the liner and out into the formation. The preferred manner of providing for such injection is simply closing valve 43 to close off the casing tubin annulus to thus force steam through such perforations. It IS a so possible, of course, to locate packing means down the well adjacent the top of the producing formation, such packing means having a closable passage for steam passage therethrough during the time that steam is circulated to heat the liner. After the liner temperature has been elevated the desired amount, the packing means are simply set to close off the flow path and steam is forced into the formation through the perforated liner.

As indicated above, the method of the present invention promotes substantially uniform steam injection over the entire portion ofa producing formation adjacent a liner and inhibits the passage of the majority of the steam through a thin section or interval of such a formation as has heretofore occurred. The present invention is useful in both the huff and puff" single well stimulation and in the steam drive recovery in which a number of wells are employed. Although only specific embodiments of the preferred invention have been described herein, the invention is not to be limited to only such embodiments but rather to the scope of the appended claims.

lclaim:

l. A method of improving the recovery of hydrocarbons from a hydrocarbon-bearing formation utilizing steam injection to improve the mobility of such hydrocarbons comprising the sequential steps of introducing steam into a well adjacent the lower portion of a well liner positioned against a producing formation, circulating said steam up the well adjacent the well liner and venting substantially all of said steam to the atmosphere to uniformly increase the temperature of said liner to approximately the temperature of the injected steam prior to injecting steam through said liner into said formation and after the temperature of said liner is so elevated, then injecting steam through said liner into the producing formation to assist the production of oil from said formation.

2. A method of improving the recovery of oil from a hydrocarbon-bearing formation penetrated by a well and having a perforated liner in said well adjacent said formation comprising the sequential steps of providing a flow path from the surface to a location adjacent the lower portion of a perforated well liner, providing a second flow path from said lower portion of said well liner to the surface, injecting steam down said first flow path into said well adjacent the lower portion of said liner, circulating said steam up said second flow path in said well adjacent said liner and venting substantially all of said steam to atmosphere to elevate the temperature of said liner to approximately the temperature of the injected steam prior to injecting steam out through said liner into said formation, closing in said second flow path, then injecting steam through said first flow path into said well through said perforations and into said formation and recovering oil from said formation. 

2. A method of improving the recovery of oil from a hydrocarbon-bearing formation penetrated by a well and having a perforated liner in said well adjacent said formation comprising the sequential steps of providing a flow path from the surface to a location adjacent the lower portIon of a perforated well liner, providing a second flow path from said lower portion of said well liner to the surface, injecting steam down said first flow path into said well adjacent the lower portion of said liner, circulating said steam up said second flow path in said well adjacent said liner and venting substantially all of said steam to atmosphere to elevate the temperature of said liner to approximately the temperature of the injected steam prior to injecting steam out through said liner into said formation, closing in said second flow path, then injecting steam through said first flow path into said well through said perforations and into said formation and recovering oil from said formation. 